Oscillating circuit with differential varactor circuits

ABSTRACT

Aspects of the present disclosure provide an oscillating circuit. An example oscillating circuitry generally includes a differential control pair comprising a first control node and a second control node. The oscillating circuit further includes a first voltage-controlled oscillator (VCO) comprising a first differential varactor circuit having a first positive control input coupled to the first control node and a first negative control input coupled to the second control node. The oscillating circuit also includes a second differential varactor circuit having a second positive control input coupled to the second control node and a second negative control input coupled to the first control node.

BACKGROUND Field of the Disclosure

Certain aspects of the present disclosure generally relate to electroniccircuits and, more particularly, to an oscillating circuit implementedwith two differential varactor circuits inverted with respect to oneanother.

Description of Related Art

In certain cases, a wireless communication device may include a radiofrequency (RF) transceiver (also referred to as a radio frequencyfront-end) for transmitting and/or receiving RF signals. Wirelesscommunication devices are widely deployed to provide variouscommunication services such as telephony, video, data, messaging,broadcasts, and so on. Such wireless communication devices may transmitand/or receive RF signals via any of various suitable radio accesstechnologies (RATs) including, but not limited to, 5G New Radio (NR),Long Term Evolution (LTE), Code Division Multiple Access (CDMA), TimeDivision Multiple Access (TDMA), Wideband CDMA (WCDMA), Global Systemfor Mobility (GSM), Bluetooth, Bluetooth Low Energy (BLE), ZigBee,wireless local area network (WLAN) RATs (e.g., Wi-Fi), and the like.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description,” one will understand how thefeatures of this disclosure provide advantages that include anoscillating circuit with a desirable frequency response acrossdifferential outputs of the oscillating circuit.

Certain aspects of the present disclosure provide an oscillatingcircuit. The oscillating circuit generally includes a differentialcontrol pair comprising a first control node and a second control node.The oscillating circuit further includes a first voltage-controlledoscillator (VCO) comprising a first differential varactor circuit havinga first positive control input coupled to the first control node and afirst negative control input coupled to the second control node. Theoscillating circuit also includes a second differential varactor circuithaving a second positive control input coupled to the second controlnode and a second negative control input coupled to the first controlnode.

Certain aspects of the present disclosure provide a radio frequencyfront-end (RFFE) integrated circuit (IC) comprising the oscillatingcircuit described herein. A transmit path or a receive path of the RFFEIC is coupled to the first VCO having the first differential varactorcircuit.

Certain aspects of the present disclosure provide a method of generatingan oscillating signal. The method generally includes applying adifferential control signal to a differential control pair coupled to afirst VCO comprising a first differential varactor circuit, thedifferential control pair comprising a first control node coupled to afirst positive control input of the first differential varactor circuitand a second control node coupled to a first negative control input ofthe first differential varactor circuit. The method further includesgenerating the oscillating signal from the first VCO based on thedifferential control signal, wherein a frequency response of the firstVCO is affected by a second differential varactor circuit having asecond positive control input coupled to the second control node and asecond negative control input coupled to the first control node.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a block diagram of an example radio frequency transceiver, inaccordance with certain aspects of the present disclosure.

FIG. 2 is a block diagram of an example frequency synthesizer having adifferentially tuned voltage-controlled oscillator, in accordance withcertain aspects of the present disclosure.

FIG. 3 is a block diagram of an example oscillating circuit withdifferential varactor circuits coupled anti-parallel to one another, inaccordance with certain aspects of the present disclosure.

FIGS. 4A-4C are schematic diagrams of example differential varactorcircuits coupled anti-parallel to one another, in accordance withcertain aspects of the present disclosure.

FIG. 5 is a flow diagram of example operations for generating anoscillating signal, in accordance with certain aspects of the presentdisclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Certain aspects of the present disclosure relate to an oscillatingcircuit and a method of generating an oscillating signal, for example,with an oscillating circuit.

Generally speaking, differential circuit structures are favored due toimproved immunity to interference (such as interference from acommon-mode signal) and greater signal range. For example, various chipsuse a switched-mode power supply (SMPS) to convert a battery voltage toa lower voltage. The power supplies may produce noise that can interferewith various components, such as a phase-locked loop (PLL), and degradeperformance. Differential structures can increase a signal range withoutincreasing supply voltage, which is beneficial for certain semiconductorprocesses having lower voltage supplies.

As an example, a differentially tuned voltage-controlled oscillator(VCO) allows for a differential PLL, which provides improved immunity tointerference and a greater signal range. In aspects, a passive filter inthe PLL can be made with half the capacitance of an equivalentsingle-ended design. A differentially tuned VCO may employ adifferential varactor circuit as the control input to adjust thefrequency of the VCO. A differential varactor circuit may usemetal-oxide-semiconductor field-effect transistor (MOSFET) or junctionvaractors. The MOSFET varactors may be n-type metal-oxide-semiconductor(NMO S) or p-type metal-oxide-semiconductor (PMOS) varactors.

A differential varactor can be made by flipping the connections of thevaractors (for example, as described herein with respect to FIGS. 4A and4B) or by using complementary varactor types (NMOS and PMOS) (forexample, as described herein with respect to FIG. 4C). In the case of anNMOS/PMOS structure, one differential input connects to a PMOS gatewhile the other differential input connects to an NMOS gate. In the caseof a flipped varactor structure, one differential input drives a gatewhile the other differential input drives a well.

As such, the differential inputs of the varactor circuit are notidentical, which may result in various performance issues. For example,leakage currents may be different for each of the differential inputsdue to different leakage current into well connections than gateconnections or different gate oxide leakage between NMOS and PMOSdevices. In certain cases, the capacitance may be different for each ofthe differential inputs. For instance, capacitance may not be the samefor different varactor types or different varactor connections (gateversus well). As a result, control input capacitance may influence thefrequency response of loop. For example, the differing leakage currentsand/or input capacitances may result in differing frequency responses onthe output polarities, which may lead to a common-mode signal leakingthrough the differential varactor circuit at certain frequencies. Incertain cases, an intermediate frequency (IF) or crystal referencefrequency may be within the frequency range where the common-mode signalcan leak through the differential varactor, which may lead to degradedperformance.

Certain aspects of the present disclosure relate to an oscillatingcircuit with differential varactor circuits coupled anti-parallel withrespect to one another, such that corresponding polarities are inverted.For example, the oscillating circuit may have a differential controlpair where the inputs of a pair of differential varactor circuits arecoupled to the differential control pair in an inverted scheme withrespect to one another. As an example, an NMOS input of a firstdifferential varactor circuit may be coupled to a PMOS input of a seconddifferential varactor circuit, and the PMOS input of the firstdifferential varactor circuit may be coupled to the NMOS input of thesecond differential varactor circuit.

In certain cases, wireless communication devices may have multiple VCOs,such as a VCO for a transmit (TX) path and another VCO for a receive(RX) path. Assuming the PLL filter is shared between the TX and RXpaths, the tune controls of the VCOs may be connected together, asfurther described herein with respect to FIG. 3. The differentialvaractor circuits from the two VCO may be coupled in anti-parallel suchthat one varactor circuit is inverted relative to the other varactorcircuit. The inverted parallel connections of the differential varactorcircuits as further described herein may balance or at least adjust thediffering leakage currents and/or input capacitances of the differentialvaractor circuits, such that the differential control may besymmetrical. In certain cases, the inverted parallel connections of thedifferential varactor circuits may provide a desirable frequencyresponse from the differential varactor circuits without an interferingcommon-mode signal at certain frequency ranges, such as the IF orcrystal reference frequency.

In certain aspects, a wireless communication device may employ a singleVCO. In such a case, the transceiver circuit may be equipped with adummy varactor circuit to provide the symmetry at the control inputs asfurther described herein.

Example RF Transceiver

FIG. 1 is a block diagram of an example RF transceiver circuit 100, inaccordance with certain aspects of the present disclosure. The RFtransceiver circuit 100 includes at least one transmit (TX) path 102(also known as a transmit chain) for transmitting signals via one ormore antennas 106 and at least one receive (RX) path 104 (also known asa receive chain) for receiving signals via the antennas 106. When the TXpath 102 and the RX path 104 share an antenna 106, the paths may beconnected with the antenna via an interface 108, which may include anyof various suitable RF devices, such as a switch, a duplexer, adiplexer, a multiplexer, and the like.

Receiving in-phase (I) or quadrature (Q) baseband analog signals from adigital-to-analog converter (DAC) 110, the TX path 102 may include abaseband filter (BBF) 112, a mixer 114, a driver amplifier (DA) 116, anda power amplifier (PA) 118. The BBF 112, the mixer 114, the DA 116, andthe PA 118 may be included in a radio frequency integrated circuit(RFIC).

The BBF 112 filters the baseband signals received from the DAC 110, andthe mixer 114 mixes the filtered baseband signals with a transmit localoscillator (LO) signal to convert the baseband signal of interest to adifferent frequency (e.g., upconvert from baseband to a radiofrequency). This frequency conversion process produces the sum anddifference frequencies between the LO frequency and the frequencies ofthe baseband signal of interest. The sum and difference frequencies arereferred to as the beat frequencies. The beat frequencies are typicallyin the RF range, such that the signals output by the mixer 114 aretypically RF signals, which may be amplified by the DA 116 and/or by thePA 118 before transmission by the antenna 106.

The RX path 104 may include a low noise amplifier (LNA) 124, a mixer126, and a baseband filter (BBF) 128. The LNA 124, the mixer 126, andthe BBF 128 may be included in a RFIC, which may or may not be the sameRFIC that includes the TX path components. RF signals received via theantenna 106 may be amplified by the LNA 124, and the mixer 126 mixes theamplified RF signals with a receive local oscillator (LO) signal toconvert the RF signal of interest to a different baseband frequency(e.g., downconvert). The baseband signals output by the mixer 126 may befiltered by the BBF 128 before being converted by an analog-to-digitalconverter (ADC) 130 to digital I or Q signals for digital signalprocessing.

Certain transceivers may employ frequency synthesizers with avariable-frequency oscillator (e.g., a voltage-controlled oscillator(VCO) or a digitally controlled oscillator (DCO)) to generate a stable,tunable LO with a particular tuning range. Thus, the transmit LO may beproduced by a TX frequency synthesizer 120, which may be buffered oramplified by amplifier 122 before being mixed with the baseband signalsin the mixer 114. Similarly, the receive LO may be produced by an RXfrequency synthesizer 132, which may be buffered or amplified byamplifier 134 before being mixed with the RF signals in the mixer 126.For certain aspects, a single frequency synthesizer may be used for boththe TX path 102 and the RX path 104. In aspects, the TX frequencysynthesizer 120 and/or RX frequency synthesizer 132 may include afrequency multiplier, such as a frequency doubler, that is driven by anoscillator (e.g., a VCO) in the frequency synthesizer. In certain cases,the VCO(s) of the TX frequency synthesizer 120 and/or RX frequencysynthesizer 132 may have differential varactors coupled in anti-parallelas further described herein with respect to FIG. 3. The invertedparallel connections of the differential varactor circuits mayfacilitate a desirable frequency response from the differential varactorcircuits.

A controller 136 may direct the operation of the RF transceiver circuit100, such as transmitting signals via the TX path 102 and/or receivingsignals via the RX path 104. The controller 136 may be a processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device (PLD), discrete gate or transistor logic,discrete hardware components, or any combination thereof. The memory 138may store data and program codes for operating the RF transceivercircuit 100. The controller 136 and/or memory 138 may include controllogic.

FIG. 2 is a block diagram of an example frequency synthesizer 200, inaccordance with certain aspects of the present disclosure. As shown, thefrequency synthesizer 200 includes a differentially tuned VCO 202, afrequency divider 204, a reference oscillator 206, a phase frequencydetector (PFD) 208, and a low-pass filter 210. The VCO 202 has adifferential control pair 212 and a differential output pair 214. TheVCO 202 includes an adjustable tuning element (not shown) such as avaractor diode or a differential varactor circuit as further describedherein with respect to FIG. 3. The frequency divider 204 may downconvertor divide the differential output of the VCO 202 to a lower frequency.The PFD 208 compares the frequency and phase of the downconverted VCOoutput to the output of the reference oscillator 206. The PFD 208outputs a current signal proportional to the error (e.g., difference)between the downconverted VCO output and the reference oscillator 206,and the low-pass filter 210 converts the PFD output to a control voltagesignal, such as a differential control voltage applied to the controlpair 212.

The feedback from the VCO 202 provides a phase-locked loop (PLL) circuitwhich tracks the error between the divided VCO output and the referenceoscillator 206, such that the VCO output is locked to the frequency andphase of the reference oscillator 206. The frequency divider 204 enablesthe frequency synthesizer 200 to generate multiple output frequencies.For example, the frequency divider 204 may be a programmable counterwhich outputs a signal at various slower frequencies than the frequencyof the VCO output. As the PFD 208 outputs a signal proportional to theerror between the downconverted VCO output and reference oscillator 206,the VCO output may be a multiple of the reference oscillator 206.

While FIGS. 1 and 2 provide an RF transceiver and frequency synthesizeras an example application in which certain aspects of the presentdisclosure may be implemented to facilitate understanding, certainaspects described herein related to an oscillating circuit having adifferential varactor circuit may be utilized in various other suitableelectronic systems.

Example Oscillating Circuit

FIG. 3 is a block diagram of an oscillating circuit 300, in accordancewith certain aspects of the present disclosure. As shown, theoscillating circuit 300 includes a differential control pair 302 and afirst VCO 304, which includes a first differential varactor circuit 306.The oscillating circuit 300 also includes a second differential varactorcircuit 308, which may be a stand-alone varactor circuit (e.g., a dummyvaractor circuit without a corresponding VCO) or implemented in a secondVCO 310 (for example, in cases where the first VCO 304 and second VCO310 are coupled to a TX path and a RX path, respectively).

The differential control pair 302 includes a first control node 312 anda second control node 314. Control signals on the first and secondcontrol nodes 312, 314 may be used to adjust the frequency of the firstVCO 304 and/or the second VCO 310. In certain aspects, the differentialcontrol pair 302 may be coupled to a low-pass filter (e.g., the low-passfilter 210) of a PLL frequency synthesizer, such as the frequencysynthesizer 200.

The first VCO 304 is an electronic oscillator with an oscillationfrequency that is controlled by an input voltage (namely, the controlsignals on the differential control pair 302). The first VCO 304 mayhave a differential output with a first positive output 316 and a firstnegative output 318. In this example, the first VCO 304 is adifferentially tuned VCO, where the first differential varactor circuit306 serves as a differential tuning element for the first VCO 304. Thatis, the first differential varactor circuit 306 provides avoltage-dependent capacitance, which is used to adjust the oscillationfrequency of the first VCO 304. The first differential varactor circuit306 may be implemented with complementary varactors (e.g., NMOS and PMOSvaractors) or with inverted pairs of homogenous varactors, as furtherdescribed herein with respect to FIGS. 4A-4C.

The first differential varactor circuit 306 includes a first positivecontrol input 320 (labeled “V_(P)”) coupled to the first control node312 and a first negative control input 322 (labeled “V_(N)”) coupled tothe second control node 314. The first positive and negative controlinputs 320, 322 of the first differential varactor circuit 306 aredifferential tuning inputs of the first VCO 304.

The second differential varactor circuit 308 may be a dummy varactorcircuit without a corresponding VCO. In such a case, the seconddifferential varactor circuit 308 may serve solely as a circuit thatbalances or adjusts the frequency response of the differential outputsof the first differential varactor circuit 306. In other cases, thesecond differential varactor circuit 308 may be implemented in thesecond VCO 310, such that the second differential varactor circuit 308may serve as a differential tuning element of the second VCO 310, aswell as a circuit that balances or adjusts the frequency response of thedifferential outputs of the first differential varactor circuit 306.Similarly, the first differential varactor circuit 306 may serve as acircuit that balances or adjusts the frequency response of thedifferential outputs of the second differential varactor circuit 308.

The second differential varactor circuit 308 may be implemented withcomplementary varactors or with inverted pairs of homogenous varactors.In certain cases, the second differential varactor circuit 308 may usethe same varactor structure as the first differential varactor circuit306. For example, the first differential varactor circuit 306 and thesecond differential varactor circuit 308 may both include complementaryvaractors (e.g., NMOS and PMOS varactors), and the second differentialvaractor circuit 308 may include complementary varactors. In othercases, the first and second differential varactor circuits comprisehomogenous varactors (e.g., all NMOS varactors).

The second differential varactor circuit 308 includes a second positivecontrol input 324 coupled to the second control node 314 and a secondnegative control input 326 coupled to the first control node 312.Expressed another way, the first differential varactor circuit 306 andsecond differential varactor circuit 308 are coupled in parallel at thecontrol pair 302 with inverted polarities. That is, the first positivecontrol input 320 of the first differential varactor circuit 306 iscoupled to the second negative control input 326 of the seconddifferential varactor circuit 308, and the first negative control input322 of the first differential varactor circuit 306 is coupled to thesecond positive control input 324 of the second differential varactorcircuit 308.

The second VCO 310 may have a differential output with a second positiveoutput 328 and a second negative output 330. The second VCO 310 may be adifferentially tuned VCO, where the second differential varactor circuit308 serves as a differential tuning element for the second VCO 310. Thesecond positive and negative control inputs 324, 326 of the seconddifferential varactor circuit 308 may be differential tuning inputs ofthe second VCO 310.

In certain aspects, an RFIC (such as an RF front-end (RFFE) IC or an RFtransceiver IC) may include the oscillating circuit 300. For example, anRF transceiver may include an RF synthesizer, which employs theoscillating circuit 300 as a differentially tuned oscillator. In certainaspects, a TX path or a RX path of the RFIC may be coupled to the firstVCO 304 having the first differential varactor circuit 306. That is, thedifferential outputs of the first VCO 304 may be coupled to a TX path ora RX path of an RF transceiver circuit. In certain cases, the RFIC mayfurther include the second VCO 310, where the TX path of the RFIC iscoupled to the first VCO 304, and the RX path is coupled to the secondVCO 310. For example, the differential outputs of the first VCO 304 maybe coupled to the TX path of an RF transceiver circuit, whereas thedifferential outputs of the second VCO 310 may be coupled to the RX pathof the RF transceiver circuit, or vice versa.

In certain aspects, the differential varactor circuits may includeinverted pairs of homogenous varactors. FIG. 4A is a schematic diagramof example differential varactor circuits coupled anti-parallel to oneanother and implemented with NMOS varactors, in accordance with certainaspects of the present disclosure. As shown, the first differentialvaractor circuit 402A includes a first varactor 404, a second varactor406, a third varactor 408, and a fourth varactor 410, each of which isan NMOS varactor. The first negative control input 412 of the firstdifferential varactor circuit 402A is coupled between well connectionsof the first varactor 404 and the second varactor 406. The firstpositive control input 414 of the first differential varactor circuit402A is coupled between gate connections of the third varactor 408 andthe fourth varactor 410. The first differential varactor circuit 402Ahas differential outputs with a first positive output 416 and a firstnegative output 418.

The second differential varactor circuit 420A includes a fifth varactor422, a sixth varactor 424, a seventh varactor 426, and an eighthvaractor 428, each of which is an NMOS varactor. The second negativecontrol input 430 of the second differential varactor circuit 420A iscoupled between well connections of the fifth varactor 422 and the sixthvaractor 424. The second positive control input 432 of the seconddifferential varactor circuit 420A is coupled between gate connectionsof the seventh varactor 426 and the eighth varactor 428. The seconddifferential varactor circuit 420A has differential outputs with asecond positive output 436 and a second negative output 438.

FIG. 4B is a schematic diagram of example differential varactor circuitscoupled anti-parallel to one another and implemented with PMOSvaractors, in accordance with certain aspects of the present disclosure.As shown, the first differential varactor circuit 402B and the seconddifferential varactor circuit 420B may have the same circuitconfiguration as depicted in FIG. 4A, except the varactors are PMOSvaractors.

In certain cases, the positive and negative control inputs may bereversed. For example, the first negative control input 412 of the firstdifferential varactor circuit 402A, 402B may be coupled between gateconnections of the third varactor 408 and the fourth varactor 410, thefirst positive control input 414 of the first differential varactorcircuit 402A, 402B may be coupled between well connections of the firstvaractor 404 and the second varactor 406, the second negative controlinput 430 of the second differential varactor circuit 420A, 420B may becoupled between gate connections of the seventh varactor 426 and theeighth varactor 428, and the second positive control input 432 of thesecond differential varactor circuit 420A, 420B may be coupled betweenwell connections of the fifth varactor 422 and the sixth varactor 424.

In certain aspects, the differential varactor circuits may includecomplementary varactors. FIG. 4C is a schematic diagram of exampledifferential varactor circuits coupled anti-parallel to one another andimplemented with complementary varactors, in accordance with certainaspects of the present disclosure. As shown, the first varactor 404, thesecond varactor 406, the fifth varactor 422, and the sixth varactor 424are NMOS varactors, whereas the third varactor 408, the fourth varactor410, the seventh varactor 426, and the eighth varactor 428 are PMOSvaractors. In this example, the first negative control input 412 of thefirst differential varactor circuit 402C is coupled between wellconnections of the first varactor 404 and the second varactor 406 (whichare NMOS varactors), the first positive control input 414 of the firstdifferential varactor circuit 402C is coupled between well connectionsof the third varactor 408 and the fourth varactor 410 (which are PMOSvaractors), the second negative control input 430 of the seconddifferential varactor circuit 420C is coupled between well connectionsof the fifth varactor 422 and the sixth varactor 424 (which are NMOSvaractors), and the second positive control input 432 of the seconddifferential varactor circuit 420C is coupled between well connectionsof the seventh varactor 426 and the eighth varactor 428 (which are PMOSvaractors).

The inverted polarities of the differential varactor circuits (402A-C or420A-C) coupled in parallel may balance or adjust the differing leakagecurrents and/or input capacitances of the differential varactorcircuits, such that the frequency response of one of the differentialvaractor circuits is symmetrical or similar across the differentialoutputs. For example, suppose the first differential varactor circuit402A is being used to tune the frequency output of a VCO (such as thefirst VCO 304). The gate connections of the seventh and eighth varactors426, 428 may balance or adjust the differing leakage currents and/orinput capacitances at the well connections of the first and secondvaractors 404, 406. Similarly, the well connections of the fifth andsixth varactors 422, 424 may balance or adjust the differing leakagecurrents and/or input capacitances at the gate connections of the thirdand fourth varactors 408, 410. In other words, the second differentialvaractor circuit may serve as a circuit that balances or adjusts thefrequency response of the first differential varactor circuit, when thefirst differential varactor circuit is being used to tune the outputfrequency of a VCO, or vice versa.

FIG. 5 is a flow diagram of example operations 500 for generating anoscillating signal, in accordance with certain aspects of the presentdisclosure. The operations 500 may be performed by an oscillatingcircuit, such as the oscillating circuit 300.

The operations 500 may begin at block 502, where a differential controlsignal is applied to a differential control pair (e.g., the differentialcontrol pair 302) coupled to a first voltage-controlled oscillator (VCO)(e.g., the first VCO 304) comprising a first differential varactorcircuit (e.g., the first differential varactor circuit 306). Thedifferential control pair includes a first control node (e.g., the firstcontrol node 312) coupled to a first positive control input (e.g., thefirst positive control input 320) of the first differential varactorcircuit and a second control node (e.g., the second control node 314)coupled to a first negative control input (e.g., the first negativecontrol input 322) of the first differential varactor circuit. At block504, the oscillating signal is generated from the first VCO based on thedifferential control signal, where a frequency response of the first VCOis affected by a second differential varactor circuit (e.g., the seconddifferential varactor circuit 308) having a second positive controlinput (e.g., the second positive control input 324) coupled to thesecond control node and a second negative control input (e.g., thesecond negative control input 326) coupled to the first control node.

In certain cases, the second differential varactor circuit may provide abalanced or desirable frequency response at both differential outputs ofthe first differential varactor circuit. For example, the frequencyresponses may be identical at both differential outputs of the firstdifferential varactor circuit. In other words, the frequency response ofthe first differential varactor circuit (such as the frequency responseat each of the differential outputs) is affected by the seconddifferential varactor circuit, such that variations between thefrequency responses of the differential outputs of the firstdifferential varactor circuit are negligible or reduced. In certaincases, the second differential varactor circuit may also facilitatesuppression of the common-mode signal, for example, at a desirable level(e.g., <−80 dB) to prevent or reduce interference from the common-modesignal on the differential outputs of the first differential varactorcircuit. In other words, the frequency response of the firstdifferential varactor circuit (such as the frequency response at each ofthe differential outputs) is affected by the second differentialvaractor circuit, such that the frequency response of the common-modesignal across the differential outputs of the first differentialvaractor circuit is suppressed or reduced.

In certain aspects, the first differential varactor circuit may be atuning element of the first VCO. For example, applying the differentialcontrol signal at block 502 may include differentially tuning the firstVCO, such as in a PLL circuit as described herein with respect to FIG.2.

In certain aspects, the second differential varactor circuit may beincluded in a second VCO. In certain cases, applying the differentialcontrol signal at block 502 may include differentially tuning the secondVCO. The operations 500 may further include generating anotheroscillating signal from the second VCO based on the differential controlsignal, where a frequency response of the second VCO is affected by thefirst differential varactor circuit.

Based on the present disclosure, it should be appreciated that theoscillating circuit described herein may enable a desirable frequencyresponse from the differential varactor circuits without an interferingcommon-mode signal at certain frequency ranges, such as the IF orcrystal reference frequency (e.g., the reference oscillator 206).

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in some other examples. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition to,or other than, the various aspects of the disclosure set forth herein.It should be understood that any aspect of the disclosure disclosedherein may be embodied by one or more elements of a claim. The word“exemplary” is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication-specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes, and variations may be made in the arrangement, operation, anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

The invention claimed is:
 1. An oscillating circuit, comprising: adifferential control node pair comprising a first control node and asecond control node; a first voltage-controlled oscillator (VCO)comprising a first differential varactor circuit having a first positivecontrol input coupled to the first control node and a first negativecontrol input coupled to the second control node; and a second VCOcomprising a second differential varactor circuit having a secondpositive control input coupled to the second control node and a secondnegative control input coupled to the first control node.
 2. Theoscillating circuit of claim 1, wherein the first positive and negativecontrol inputs of the first differential varactor circuit aredifferential tuning inputs of the first VCO.
 3. The oscillating circuitof claim 1, wherein the second positive and negative control inputs ofthe second differential varactor circuit are differential tuning inputsof the second VCO.
 4. The oscillating circuit of claim 1, wherein: thefirst differential varactor circuit includes complementary varactors;and the second differential varactor circuit includes complementaryvaractors.
 5. The oscillating circuit of claim 1, wherein: at least oneof the first differential varactor circuit or the second differentialvaractor circuit comprises a first n-type metal-oxide-semiconductor(NMOS) varactor, a second NMOS varactor, a first p-typemetal-oxide-semiconductor (PMOS) varactor, and a second PMOS varactor;at least one of the first positive control input of the firstdifferential varactor circuit or the second positive control input ofthe second differential varactor circuit is coupled between the firstNMOS varactor and the second NMOS varactor; and at least one of thefirst negative control input of the first differential varactor circuitor the second negative control input of the second differential varactorcircuit is coupled between the first PMOS varactor and the second PMOSvaractor.
 6. The oscillating circuit of claim 1, wherein: at least oneof the first differential varactor circuit or the second differentialvaractor circuit comprises a first NMOS varactor, a second NMOSvaractor, a first PMOS varactor, and a second PMOS varactor; at leastone of the first positive control input of the first differentialvaractor circuit or the second positive control input of the seconddifferential varactor circuit is coupled between the first PMOS varactorand the second PMOS varactor; and at least one of the first negativecontrol input of the first differential varactor circuit or the secondnegative control input of the second differential varactor circuit iscoupled between the first NMOS varactor and the second NMOS varactor. 7.The oscillating circuit of claim 1, wherein the first and seconddifferential varactor circuits comprise a same type of varactor circuit.8. The oscillating circuit of claim 7, wherein: the first differentialvaractor circuit includes a first varactor, a second varactor, a thirdvaractor, and a fourth varactor; the second differential varactorcircuit includes a fifth varactor, a sixth varactor, a seventh varactor,and an eighth varactor; the first positive control input of the firstdifferential varactor circuit is coupled between well connections of thefirst varactor and the second varactor; the first negative control inputof the first differential varactor circuit is coupled between gateconnections of the third varactor and the fourth varactor; the secondpositive control input of the second differential varactor circuit iscoupled between well connections of the fifth varactor and the sixthvaractor; and the second negative control input of the seconddifferential varactor circuit is coupled between gate connections of theseventh varactor and the eighth varactor.
 9. The oscillating circuit ofclaim 7, wherein: the first differential varactor circuit includes afirst varactor, a second varactor, a third varactor, and a fourthvaractor; the second differential varactor circuit includes a fifthvaractor, a sixth varactor, a seventh varactor, and an eighth varactor;the first positive control input of the first differential varactorcircuit is coupled between gate connections of the first varactor andthe second varactor; the first negative control input of the firstdifferential varactor circuit is coupled between well connections of thethird varactor and the fourth varactor; the second positive controlinput of the second differential varactor circuit is coupled betweengate connections of the fifth varactor and the sixth varactor; and thesecond negative control input of the second differential varactorcircuit is coupled between well connections of the seventh varactor andthe eighth varactor.
 10. The oscillating circuit of claim 1, wherein: atleast one of the first differential varactor circuit or the seconddifferential varactor circuit comprises a first NMOS varactor, a secondNMOS varactor, a third NMOS varactor, and a fourth NMOS varactor; atleast one of the first positive control input of the first differentialvaractor circuit or the second positive control input of the seconddifferential varactor circuit is coupled between the first NMOS varactorand the second NMOS varactor; and at least one of the first negativecontrol input of the first differential varactor circuit or the secondnegative control input of the second differential varactor circuit iscoupled between the third NMOS varactor and the fourth NMOS varactor.11. The oscillating circuit of claim 1, wherein: at least one of thefirst differential varactor circuit or the second differential varactorcircuit comprises a first PMOS varactor, a second PMOS varactor, a thirdPMOS varactor, and a fourth PMOS varactor; at least one of the firstpositive control input of the first differential varactor circuit or thesecond positive control input of the second differential varactorcircuit is coupled between the first PMOS varactor and the second PMOSvaractor; and at least one of the first negative control input of thefirst differential varactor circuit or the second negative control inputof the second differential varactor circuit is coupled between the thirdPMOS varactor and the fourth PMOS varactor.
 12. A radio frequencyfront-end (RFFE) integrated circuit (IC) comprising the oscillatingcircuit of claim 1, wherein a transmit path or a receive path of theRFFE IC is coupled to the first VCO having the first differentialvaractor circuit.
 13. The RFFE IC of claim 12, wherein the transmit pathof the RFFE IC is coupled to the first VCO and wherein the receive pathis coupled to the second VCO.
 14. A method of generating an oscillatingsignal, comprising: applying a differential control signal to adifferential control node pair coupled to a first voltage-controlledoscillator (VCO) comprising a first differential varactor circuit, thedifferential control node pair comprising a first control node coupledto a first positive control input of the first differential varactorcircuit and a second control node coupled to a first negative controlinput of the first differential varactor circuit; and generating theoscillating signal from the first VCO based on the differential controlsignal, wherein a frequency response of the first VCO is affected by asecond differential varactor circuit having a second positive controlinput coupled to the second control node and a second negative controlinput coupled to the first control node and wherein applying thedifferential control signal comprises differentially tuning a second VCOcomprising the second differential varactor circuit.
 15. The method ofclaim 14, wherein applying the differential control signal comprisesdifferentially tuning the first VCO.
 16. The method of claim 14,wherein: applying the differential control signal comprisesdifferentially tuning a second VCO comprising the second differentialvaractor circuit; and the method further comprises generating anotheroscillating signal from the second VCO based on the differential controlsignal, wherein a frequency response of the second VCO is affected bythe first differential varactor circuit.
 17. The method of claim 14,wherein the first and second differential varactor circuits comprise asame type of varactor circuit.